Multivibrator



Nov. 30, 1954 a. H. NIBBE MULTIVIBRATOR Filed May 15. 1946 POSITIVE VOLTAGE SUP {25 NEGATIVE VOLTAGE SUPPLY INVENTOR GEORGE H. NIBBE ATTORNEY United States Patent MULTIVIBRATOR George H. Nibbe, Chicago, IlL, assignor, by mesne assignments, to the United States of America as represented by the Secretary of the Navy Application May 15,1946, Serial No. 669,745 3 Claims. c1. 250-46) This invention relatesv to.multivibrator.s and more particularly to multivibrators: having amplified: time constants.

In the conventional free; running multivibrator, the length of the conducting period for'each tube is. mainly dependent upon. the resistance and. capacitance in the control grid circuit of the. other tube... The. conducting periodsof the tubes determinethe ferquency of; the. rectangular voltage wave outputsandalso the. ratio between the positive portion of the wave and the negative portion. In order to obtain long periods of conduction: for either. tube or a low frequency ofoperation in this type of multivibrator, it becomes necessary to use large capacitors and resistors in the grid circuit of either or. both' of the tubes.

In the present invention amultivibratorv is.proposed in which the plate conduction-period for. either or both of the tubes may be either an exceedingly long time, or a fairly long period with small circuit elements for designs where space is at a premium. Another feature of the present invention is that the plate voltage of the conducting tube has a linear rate of, change. and thus thecircuit may be used to supply either a sawtooth or a. square wave voltage wave form.

A primary object of the present invention is to generally improve multivibrators.

Another object of this invention is to provide a multivibrator capable of producing extremely low frequency square wave voltages.

A further object is to provide a multivibrator capable of producing square wave voltage gates having very long time durations.

A still further object is to provide a multivibrator capable of producing linear sawtooth voltage outputs.

These and other objects of the invention will be apparent from the following description when taken with the accompanying drawing which is a schematic diagram of one embodiment thereof.

Referring to the drawing, pentode electron tubes 11 and 12 are multivibrator tubes having their plate circuits alternately conducting and non-conducing. The anode 11A of pentode 11 is connected to the positive voltage supply at terminal 13 through plate load resistor 14, to the suppressor grid 12B of pentode 12 through condenser 15, and to its own control grid 11D through condenser 16. The anode 12A of pentode 12 is similarly connected to the positive supply at terminal 13 through plate load resistor 20, to the suppressor grid 11B of pentode 11 through condenser 21, and to its own control grid 12D through condenser 22. The cathodes 11B and 12E of pentodes 11 and 12 are connected together and in this embodiment to ground. The control grid 11D of pentode 11 is returned to the common cathode connection through resistor 23, and the control grid 12D of pentode 12 is connected to the common cathode connection through resistor 24. A voltage divider consisting of resistors 30, 31, and 32 is connected between the positive voltage supply at terminal 13 and the negative voltage supply at terminal 25. The screen grid 11C of pentode 11 is connected to the junction A of resistors 30 and 31 and the suppressor grid 11B of pentode 11 is connected to the junction 31A of resistors 31 and 32. Condenser 33 is connected in parallel with resistor 31. Similarly resistors 40, 41, and 42 form a voltage divider between terminal 13 and terminal 25 with the screen grid 12C of pentode 12 connected to the junction A of resistors 40 and 41, the suppressor grid 12B of pentode 1 12, connected to, the, junction 41A of resistor 41 and 42, and condenser 43 connected in parallel with resistor 41.

In the operation of this. embodiment of the invention the plates 11A and 12A of pentodes 11 and 12 are alternately conducting and non-conducting. Assuming that the plate 12A of pentode 12 has just completed the non-conducting portion. of its cycle, condenser 22 is charged to the. potential of the positive voltage supply at terminal 13. When. the plate 12A of pentode 12 becomes conducting due to a positive voltage pulse on its suppressor grid 12B, the plate 11A of pentode 11 becomes non-conducting. This switching process is rapid due to regenerativeaction as explained later herein. When the plate 12A of pentode 12 becomes conducting, the plate. 12A voltage drops causing the control grid 12D of pentode 12 to drop due to coupling by condenser 22. The drop in plate 12A and control grid 12D voltages in pentode 12 continues until the. values of control grid 12D and plate. 12A voltages satisfy the conditions for one point on the load line plotted on the tube characteristics for pentode 12 with load resistor 20 and. the operating voltages present. on the other tube. elements. Condenser 22 starts discharging which raises the control grid 12D voltage and allows the plate 12A voltage of pentode 12 todrop' which coupled back to the control grid 12D of pentode 12. tends to keep the control grid 12D voltage from rising. This feed back of voltage, commonly referred to as Miller-feedback, causes the time constant of. discharge for condenser 22 to be substantially equal tothe productof. resistor 24, condenser 22 and they gain of pentode 12. As this time constant is very large, the rise of voltage at the control grid 12D of pentode 12 and the fall of voltage atthe plate 12A are very linear. The plate 12A voltage of pentode 12 drops until it approaches the voltage of the screen grid.12C of pentode 12. In this operating condition the control grid 12D voltage further increases the screen grid 12C voltage drops due to an increased screen current. A portion of this drop in screen grid 12C voltage of pentode 12 is coupled to the suppressor grid 12B of pentode 12 by the voltage divider consisting of resistors 40, 41, and 42. The lowering of suppressor grid 12B voltage causes a decrease in plate 12A conduction and a further increase in screen 12C conduction. This cumulative reaction results in the plate 12A conduction being rapidly cut off with a resulting rise in plate 12A voltage. This rise of plate 12A voltage of pentode 12 is coupled through condenser 21 as a positive voltage pulse to the suppressor grid 11B of pentode 11 causing plate 11A conduction to be initiated in pentode 11. Pentode 11 then goes through an operation identical to that described above while the plate 12A of pentode 12 remains non-conducting. At the end of the plate 11A conduction period of pentode 11, plate 12A conduction is resumed in pentode 12 and the cycle is repeated.

In the operation of this multivibrator, the plate conduction periods for pentodes 11 and 12 may be equal or unequal depending upon the time constants of the re spective pentodes. The circuit could be readily synchronized with an external source by applying a synchronizing voltage to either the screen grid or the plate of either pentode depending upon the time relations desired and the polarity of the synchronizing signal. It will be apparent to those skilled in the art that a square wave voltage output may be obtained from the screen grid or suppressor grid of either pentode and a sawtooth voltage waveform may be obtained from the plate of either pentode. A trigger voltage could likewise be obtained from the screen grid of either pentode for synchronizing other circuits.

The invention described in the foregoing specification need not be limited to the details shown, which are considered to be illustrative of one form the invention may take. The scope of the invention is defined by the appended claims.

What is claimed is:

1. An amplified time constant multivibrator comprising, first and second electron tubes each having at least a cathode, an anode, a control grid, a screen grid, and a suppressor grid, a first condenser connected between the anode and control grid of said first electron tube, a second condenser similarly connected to said second electron tube, a first resistance connected between the cathode and control grid of said first electron tube, a second resistance similarly connected to said second electron tube, a positive voltage source, said first and second condensers adapted to be charged from said positive voltage source, and to be discharged through said first and second resistors with amplified time constants, and a resistancecapacitance coupling from the anode of each of said electron tubes to the suppressor grid and screen grid of the other of said electron tubes, said resistance-capacitance coupling circuits used to initiate plate conduction in one of said electron tubes when plate conduction in the other of said electron tubes ceases, the plate conduction time for each of said electron tubes being dependent upon said amplified time constants.

2. An amplified time constant multivibrator producing sawtooth and square wave voltages of long duration comprising, first and second electron tubes having at least a cathode, an anode, a control grid, a screen grid,

and a suppressor grid, a first condenser connected between the anode and control grid of said first electron tube, a second condenser similarly connected to said second electron tube, a first resistance connected between the cathode and control grid of said first electron tube, a second resistance similarly connected to said second electron tube, a positive voltage source, said first and second condensers adapted to be charged from said positive voltage source, and to be discharged, with amplified time constants through said first and second resistors and said first and second electron tubes, a negative voltage source, a first resistance-capacitance voltage divider between said positive voltage supply and said negative voltage supply, the suppressor grid and screen grid operating potential of said first electron tube being obtained from said first resistance-capacitance voltage divider, a second resistance-capacitance voltage divider similarly connected to said second electron tube, and third and fourth condensers connected between the anode of each of said first and second electron tubes and the suppressor grid of the other, the coupling of said third and fourth con- 4 densers initiating plate conduction in one of said electron tubes when plate conduction ceases in the other, the length of period of plate conduction in each of said first and second electron tubes depending upon the amplified time constant in the control grid circuit of the electron tube having plate conduction.

3. A multivibrator comprising, first and second electron tubes, each of said electron tubes having at least an anode, a control grid, a suppressor grid and a cathode, means coupled to said tubes for alternately initiating anode conduction in said tubes, said means including, a coupling between the anode of said first tube and the suppressor grid of said second tube for initiating anode conduction in said second tube at the cessation of anode conduction in said first tube, a coupling between the anode of said second tube and the suppressor grid of said first tube for initiating anode conduction in said first tube at the cessation of anode conduction in said second tube, a first capacitor coupled between the anode and the control grid of said first tube, a first resistor coupled between the control grid and the cathode of said first tube, a second capacitor coupled between the anode and the control grid of said second tube, a second resistor coupled between the control grid and the cathode of said second tube, said first capacitor charging during the anode conduction of said second tube and discharging through said first resistor and said first tube during the anode conduction of said first tube, said second capacitor charging during the anode conduction of said first tube and discharging through said second resistor and said second tube during the anode conduction of said second tube.

References Cited in the file of this patent UNITED STATES PATENTS Number Name Date 2,212,967 White Aug. 27, 1940 2,416,513 Brown, Jr. Feb. 25, 1947 2,426,996 Goodall Sept. 9, 1947 2,549,764 Bartels Apr. 24, 1951 

